CA1038618A - Process for preparing yttrium oxide and rare earth metal oxide phosphors - Google Patents
Process for preparing yttrium oxide and rare earth metal oxide phosphorsInfo
- Publication number
- CA1038618A CA1038618A CA202,818A CA202818A CA1038618A CA 1038618 A CA1038618 A CA 1038618A CA 202818 A CA202818 A CA 202818A CA 1038618 A CA1038618 A CA 1038618A
- Authority
- CA
- Canada
- Prior art keywords
- phosphor
- atmosphere
- oxide
- heating
- activated
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
- C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
- C09K11/77—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals
- C09K11/7766—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals containing two or more rare earth metals
- C09K11/7767—Chalcogenides
- C09K11/7769—Oxides
-
- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21K—TECHNIQUES FOR HANDLING PARTICLES OR IONISING RADIATION NOT OTHERWISE PROVIDED FOR; IRRADIATION DEVICES; GAMMA RAY OR X-RAY MICROSCOPES
- G21K4/00—Conversion screens for the conversion of the spatial distribution of X-rays or particle radiation into visible images, e.g. fluoroscopic screens
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- General Engineering & Computer Science (AREA)
- High Energy & Nuclear Physics (AREA)
- Inorganic Chemistry (AREA)
- Materials Engineering (AREA)
- Organic Chemistry (AREA)
- Luminescent Compositions (AREA)
Abstract
PROCESS FOR PREPARING YTTRIUM OXIDE AND
RARE EARTH METAL OXIDE PHOSPHORS
Abstract of the Disclosure Oxide phosphors which have a host matrix of yttrium or a rare earth metal and are activated by one or more rare earth metal activators are prepared by heating a mixture of salts Or the host and activator metals (preferably this mixture is formed by co-precipitating the salts of the host and acti-vator metals) at an elevated temperature in an oxygen-containig atmosphere to form the oxide phosphor, and then heating the phosphor at an elevated temperature in a non-oxidizing atmos-phere which is free of halogenating agents, chalcogenating agents, or fluxes. The step of heating in a non-oxidizing at-mosphere brings about a substantial increase in the X-ray speed of the phosphor and aslo improves the stability of the phosphor-to light and increases its reflectance in the visible region Or the spectrum. Phosphors prepared by use of this process are useful in the manufacture of X-ray intensifying screens.
RARE EARTH METAL OXIDE PHOSPHORS
Abstract of the Disclosure Oxide phosphors which have a host matrix of yttrium or a rare earth metal and are activated by one or more rare earth metal activators are prepared by heating a mixture of salts Or the host and activator metals (preferably this mixture is formed by co-precipitating the salts of the host and acti-vator metals) at an elevated temperature in an oxygen-containig atmosphere to form the oxide phosphor, and then heating the phosphor at an elevated temperature in a non-oxidizing atmos-phere which is free of halogenating agents, chalcogenating agents, or fluxes. The step of heating in a non-oxidizing at-mosphere brings about a substantial increase in the X-ray speed of the phosphor and aslo improves the stability of the phosphor-to light and increases its reflectance in the visible region Or the spectrum. Phosphors prepared by use of this process are useful in the manufacture of X-ray intensifying screens.
Description
~0;~8618 This invention relates in general to phosphors and in particular to yttrium oxide and rare earth metal oxide phosphors. More specifically, this invention relates to a process for the preparation of phosphors having a host matrix of yttrium oxide or a rare earth metal oxide which are activated by a rare earth metal activator.
Phosphors in which the host matrix is yttrium oxide or a rare earth metal oxide such as lanthanum oxide or gadolinium oxide and the activator is a rare earth metal such as europium or terbium have been known for many years. These phosphors are useful in a variety of applications, such as in cathode ray tubes and in fluorescent lamps. They are typically prepared by the co-precipitation from solution of salts of the host and activator metals followed by heating of the precipitate in air at an elevated temperature to form the oxide phosphor. Most commonly, the phosphor is prepared by co-precipitating the oxalates of the host and activator metals, but the phosphors can also be prepared by co-precipitating other salts from which the oxides can be formed by heating in air, for example, such salts as hydroxides, carbonates, citrates, acetates, tartrates, and the like.
Suitable conditions for preparing the oxide phosphors by co-precipitating a mixture of decomposable salts and heating in air are described in many references, for example, in United States patents 3,250,722, 3,420,861, 3,449,258, 3,449,259 and 3,484,381.
It is known that an improvement in the properties of oxide phosphors of the type described above can be obtained by heating the phosphor in contact with a flux. As described in Canadian patents 779,211 and 779,860, such treatment alters -~
,., q~
Phosphors in which the host matrix is yttrium oxide or a rare earth metal oxide such as lanthanum oxide or gadolinium oxide and the activator is a rare earth metal such as europium or terbium have been known for many years. These phosphors are useful in a variety of applications, such as in cathode ray tubes and in fluorescent lamps. They are typically prepared by the co-precipitation from solution of salts of the host and activator metals followed by heating of the precipitate in air at an elevated temperature to form the oxide phosphor. Most commonly, the phosphor is prepared by co-precipitating the oxalates of the host and activator metals, but the phosphors can also be prepared by co-precipitating other salts from which the oxides can be formed by heating in air, for example, such salts as hydroxides, carbonates, citrates, acetates, tartrates, and the like.
Suitable conditions for preparing the oxide phosphors by co-precipitating a mixture of decomposable salts and heating in air are described in many references, for example, in United States patents 3,250,722, 3,420,861, 3,449,258, 3,449,259 and 3,484,381.
It is known that an improvement in the properties of oxide phosphors of the type described above can be obtained by heating the phosphor in contact with a flux. As described in Canadian patents 779,211 and 779,860, such treatment alters -~
,., q~
-2-10;~3618 the shape and particle size distribution of the phosphor crystals and bri~gs about an increase in the ef~iciency of the phosphor.
Many materials are suitable for use as a flux, for example, borax, sodium metakorate, or metal fluorides such as lithium floaride.
However, the step of heating the oxide phosphor in the presence of a flux is disadvantageous for several reasons. Thus, for example, heating the phosphor in admixture with the flux tends to cause sintering and it ordinarily becomes necessary to break up the sinter~d particles in order to provide them in a form from which satisfactory coatings can be prepared. This can be accom-plished by grinding but this invo~ves the expense and incon-venience of an additional processing step. Moreover, because of the abrasive nature of the oxide phosphor which causes the removal of metal or other contaminants from grinding and sieving equipment, such a procedure can introduce impurities into the phosphor which can result in a 108s of much of the ~peed increase that was achieved by the treatment with the flux.
In acco~dance with ~hi 5 invention, it has been discovered that yttrium oxide and rare earth metal oxide phosphors which have improved characteristics which render them e~pecially useful in radiography can be prepared by a process in which the step,df heating a mixture of host and activator salts in an oxygen-containing atmosphere, such as air, is followed by the s~ep of heating at an elevated temperature in a non-Gxmdzzing at-mosphere. The mixture of salts is preferably formed by co-precipitation. This step of heating in a non-oxidizing atmos-phere has been found to bring aboht an improvement in the X-ray speed of the phosphor and also to improve its stability to light
Many materials are suitable for use as a flux, for example, borax, sodium metakorate, or metal fluorides such as lithium floaride.
However, the step of heating the oxide phosphor in the presence of a flux is disadvantageous for several reasons. Thus, for example, heating the phosphor in admixture with the flux tends to cause sintering and it ordinarily becomes necessary to break up the sinter~d particles in order to provide them in a form from which satisfactory coatings can be prepared. This can be accom-plished by grinding but this invo~ves the expense and incon-venience of an additional processing step. Moreover, because of the abrasive nature of the oxide phosphor which causes the removal of metal or other contaminants from grinding and sieving equipment, such a procedure can introduce impurities into the phosphor which can result in a 108s of much of the ~peed increase that was achieved by the treatment with the flux.
In acco~dance with ~hi 5 invention, it has been discovered that yttrium oxide and rare earth metal oxide phosphors which have improved characteristics which render them e~pecially useful in radiography can be prepared by a process in which the step,df heating a mixture of host and activator salts in an oxygen-containing atmosphere, such as air, is followed by the s~ep of heating at an elevated temperature in a non-Gxmdzzing at-mosphere. The mixture of salts is preferably formed by co-precipitation. This step of heating in a non-oxidizing atmos-phere has been found to bring aboht an improvement in the X-ray speed of the phosphor and also to improve its stability to light
- 3 -and to increase its reflectance mn the visible region of the spectrum. AlternatiYely, satisfactory phosphors can be prepared by blending pure ~xides of the host and activator or by treating the host oxide with a solution of the activator followed by heating in air and subsequently heating at an ele~ated temp-erature in a non-~xidizing atmosphere.
More specifically, in the process of this invention the oxide phosphor is heated in a non-oxidizing atmosphere which is free of halogenating agents, chalcogenating agents lQ and fluxes. The heating is carried out at a sufficient tempera-ture and for a sufficient period of time to bring about the de-sired improvement in the properties ~f the phosphor, such as increased X-ray speed. ~he non-oxidizing atmosph~re ma~ be an inert atmosphere, such as an atmosphere composed of an inert gas such as nitrogen or argon, or a mildiy reducing atmosphere, such as an atmosphere which is a mixture of hydrogen and an inert gas.
However, when the atmosphere utilized is mildly reduced in nature, the temperature is maintained at a lower level than that which is ordinarily employed with an inert atmosphere, as hereinafter described in detail.
It should he noted that the method of this invention is distinguished from prior art processes in which a yttrium oxide or rare earth metal oxide phosphor is utilized as a , starting material to produce a different type of phosphor, since the final product produced ~y the process described herein is an oxide p~sphor but one which has impro~ed pro-perties. Thus, the heating of the oxide phosphor is carried out in an atmosphere which is free of halogenating agents, as ~ -"
More specifically, in the process of this invention the oxide phosphor is heated in a non-oxidizing atmosphere which is free of halogenating agents, chalcogenating agents lQ and fluxes. The heating is carried out at a sufficient tempera-ture and for a sufficient period of time to bring about the de-sired improvement in the properties ~f the phosphor, such as increased X-ray speed. ~he non-oxidizing atmosph~re ma~ be an inert atmosphere, such as an atmosphere composed of an inert gas such as nitrogen or argon, or a mildiy reducing atmosphere, such as an atmosphere which is a mixture of hydrogen and an inert gas.
However, when the atmosphere utilized is mildly reduced in nature, the temperature is maintained at a lower level than that which is ordinarily employed with an inert atmosphere, as hereinafter described in detail.
It should he noted that the method of this invention is distinguished from prior art processes in which a yttrium oxide or rare earth metal oxide phosphor is utilized as a , starting material to produce a different type of phosphor, since the final product produced ~y the process described herein is an oxide p~sphor but one which has impro~ed pro-perties. Thus, the heating of the oxide phosphor is carried out in an atmosphere which is free of halogenating agents, as ~ -"
- 4 -.
distinguished from prior art processes in which oxide phosphors are heated in an atmosphere containing a halogenati~g agent, such as a hydrogen halide, in order to produce an oxyhalide phosphor. It is also carried out in an atmosphere which is free of chalcogenating agents, that is agents capable of forming sulfides, selenides or tellurides, as distinguished from prior art processes in which oxide phsophors are heated in an atmosphere containing a chalcogenating agent, such as the process of heating in an atmosphere containing hydrogen sulfide to form an oxysulfide phosphor. Heating in the non-oxidizing atmosphere is also carried out in the process of this invention in the absence of a flux and the invention thereby avoids the disadvantages involved in prior art pro-cesses in which fluxes have been employed.
The phosphors to which the method of this invention is applicable are oxide phosphors which have a host matrix of yttrium or of a rare earth metal, that is, a metal having an atomic number of from 57 to 71 in the Periodic Table of the Elements. These phosphors are activated by at least one rare earth ~' metal activator preferably selected from the group consisting of europium, gadolinium, terbium or dysprosium. Typical examples of the phosphors which can be prepared in accordance with the process of this invention to provide substantial improvement in properties such as X-ray speed are europium-activated gadolinium oxide ~Gd203:Eu), terbium-activated gadolinium oxide (Gd203:Tb), dysprosium-activated gadolinium oxide (Gd203:Dy), terbium-activated yttrium oxide (Y203:Tb), gadolinium-activated yttrium oxide (Y203:Gd), europium-activated lanthanum oxide (La203:Eu) and europium-activated yttrium oxide (Y203:Eu). The activator ~
. : .
~03~3618 forms a small proportion of the total phosphor, typically from about 0.01 mole percent to about 10 mole percent.
In preparing oxide phosphors in accordance with this invention, a preferred procedure is to employ the double-run co-precipitation method of United States patent 3,668,143 to form a mixed oxalate of the host and activator metals. In accordance with this method, separate aqueous solutions, con-taining (1) oxalate anions and (2) the host and activator cations, are separately introduced into a reaction solution, an excess of up to one molar of the anions or cations is maintained in the reaction solution throughout the reaction, and local excesses of anions or cations are prevented. Reaction temperatures are preferably in the range of from about 70 C
to about 100 C. It is preferred for the purposes of this invention to carry out the co-precipitation of the oxalates in the presence of excess oxalate ion and with at least a 0.2 molar hydrogen ion concentration in the reaction solution.
The separate solutions which are added to the reaction solution preferably have a concentration of less than 1 molar and most preferably less than 0.5 molar. Optimum results are obtained if the oxalate precipitate is prepared slowly, that is, with each solution being added to the reaction solution at a rate of less than 0.1 mole per liter of reaction solution per minute.
This results in the formation of large grain size oxalates which upon subsequent heating in an oxygen-containing atmosphere followed by heating in a non-oxidizing atmosphere provide oxide phosphors with desirable crystallographic structure and grain size which exhibit very high speeds.
As previously disclosed herein, the precipitate obtained by co-precipitating salts of the host and activator 1038~i18 m~tals i5 heated in an oxxgen-contain~ng atmosphere to form ~P oxide phosphor. Under typical circumstances this heating step is carried out in air although other ox~gen-containing atmospheres such as a mixture of oxygen and an inert gas such as argon could be used if desired. The duration of heating in the oxygen-containing atmosphere will ordinarily be in ~he range from about 0.5 hours to about 10 hours and more usually from about 1 to about 3 hours. Temperatures employed in this step are typically in the range from about 700C to about 1400C and pre-ferably in the range rom about 800C to about 11~0C.
After formation of the oxide phosphor by the step of heating in an oxygen-containing atmosphere, it is heated in a non-oxidizing atmosphere to bring about the desired improvement , in properties, such as X-ray speed. The atmosphere utilized in this step is a non-oxidizing atmosphere which is free of halogenating agents, chalcogenating agents, and fluxes. It may be an inert atmosphere, such as an atmosphere composed of nitrogen or o~ one of the inert gas elements such as helium, neon, or argon. Mixtures of two or more inert gases can be `~
utilized if desired. The atmosphere can consist of the dry inert gas or of a mixture of water vapor and inert gas. As an alternative to the use of an inert atmosphere, the atmos-phere employed in thiC step can be mildly reducing in nature.
Strongly reducing atmo~pheres are preferably avoided as they render the reaction difficult tp control and can adversely affect the phosphor, particularly when very high temperatures are employed.
An example of a preferred mildly reducing atmosphere that can be empioyed with good results is a mixture of hydrogen and an inert gas, such as nitrogen or argon in which the hydrogen is present in a minor proportion (i.e., less than about 455 by volume and preferably from about 5 to about 35% by volume).
~ . . . . . . . . .. . . . .. .
103~3618 A mildly reducing atmosphere that is especially useful can also be provided by heating the oxide phosphor in the presence of carbon, such as by placing the phosphor in a carbon boat, and providing some water vapor in the atmosphere. This results in the formation of water gas in accordance with the following reactions:
C ~ H20 ~ 2 2 ~ C02 2 The mildly reducing water gas atmosphere generated by the reaction of carbon with water vapor has been found to give excellent results, especially as regards the stability to light of the resulting phosphor.
In accordance with this invention, the oxide phosphor -~
is heated at an elevated temperature in a non-oxidizing atmos-phere, free of halogenating agents, chalcogenating agents, and fluxes, under conditions of time and temperature sufficient to effect an increase in the X-ray speed of the phosphor.
Suitable temperatures for use in this step are in the range from about 400 C to about 1400 C, with the higher temperatures within this range being used when the atmosphere employed is inert and the lower temperatures within this range being used when the atmosphere employed is mildly reducing. With inert atmospheres, the preferred temperatures are in the range from about 750C to about 1200C and most preferably in the range from about 800 C to about 1000 C. With an atmosphere con-sisting of a mixture of hydrogen and an inert gas, particularly good results are obtained with temperatures of about 450C to about 600C and the optimum temperature is about 500C.
Suitable times for heating the phosphor in the non-oxidizing atmosphere will depend on the atmosphere used, the temperature, . ..
and the thickness of the phosphor layer subjected to heating, but are typically in the range from about 0.5 hours to about 8 hours and more usually from about 2 to about 4 hours.
Heating of the phosphor in the non-oxidizing atmosphere does not cause sintering as occurs when phosphors are heated in contact with fluxes in accordance with the prior art. Accord-ingly, no grinding or similar operations are required in the process of this invention.
The steps of heating in the oxygen-containing atmos-phere and heating in the non-oxidizing atmosphere can be carried out in separate furnaces and this will ordinarily be ~ ;
the most convenient procedure. Alternatively, one can employ a continuous procedure in which the precipitate is passed into a two zone furnace, the first zone containing air, or other oxygen-containing atmosphere, and the second zone containing -the non-oxidizing atmosphere.
While applicant does not wish to be bound by any theoretical explanation for the manner in which his invention functions, it is believed that the heating in an inert or mildly reducing atmosphere alters certain sites within the crystal which act as absorbing centers for light. Studies of the emission spectra of the phosphors with excitation by X-rays indicate that these spectra are essentially unaffected by heat-ing in the inert or mildly reducing atmosphere except for an overall increase in intensity.
The invention is further illustrated by the following examples of its practice.
Example A europium-activated gadolinium oxide phosphor was prepared by use of the co-precipitation procedures described in United States patent 3,668,143 as follows:
.
103861~
A solution A ~as prepared ~y mixing 375 nilliliters of 2 molar gadolinium trichloride solution, 37.5 milliliters of 0.4 molar europium trichloride solution and sufficient distilled water to make 5 liters. A solution B was prepared by mixing 1600 milliliters of 1 molar oxalic acid solution with sufficient distilled water to make 5 liters. A solu~ion C
was prepared by mixing 200 milliliters of 2 molar gddolinium trichloride solution and 20 milliliters of 0.4 molar europium trichloride solution with s~fficient distilled water to make 4 liters. Solutions A and B were heated to 80C. Solution C
was placed in t~e fluted 22 liter flask de~cribed in United States patent 3,668,143 and heated to 95C. Solutions A and B were then simultaneously added to solution C at a rate of lO0 milliliters of each per minute and solution C was vigorously stirred during the addition. When the addition was complete, the precipitate was allowed to settle and was washed four times by decantation with distilled water. It was then colleated~land dried in air at room temperature overnight. The dry precipitate was placed in a quartz tray and heated in air for 1.5 hours at a temperature of 1115C ~n a muffle furnace and then rapidly cooled in air. The phosphor obtained by this procedure was placed in a m~tal planchet in the form of a layer with a thickness of 0.07& inch and an area o~ 0.76 square inches. A similar planchet was filled with a layer of a commercially a~ailable -calcium tungst~te pho~phor. The planchets were placed close to a sheet of black and white, high-speed, pan-sensitiz~d negative fi-lm (code 2043 Tri-X* recording film manufactured by Eastman Kodak Compan~ and exposed to 70 kvp X-rays filtered by 0.5 millimeters of copper and 1 millimeter of aluminum. After exposure, the film ' , , * Tradema~k ~ 10 -; ~ ... , .:
was developed, stopped, fixed, washed and dried in the con-ventional manner. The film was also exposed through an aluminum step wedge to determine the relationship between exposure and developed density. The exposure produced by the europium-activated gadolinium oxide phosphor with excitation by the filtered 70 kvp X-rays was found to be 3.8 times that obtained with the calcium tungstate phosphor used as a control.
A ten-gram portion of the europium-activated gadolinium oxide phosphor prepared in the manner described above was placed in a glassy carbon boat and was heated for 4 hours at 825 C in a tube furnace with 1.6 cubic feet per hour of nitrogen and 2 cubic feet per hour of argon passing through the tube. Before entering the furnace, the gas stream passed through a 500-milliliter capacity gas bubbler filled with distilled water. At the end of the heating period, the sample was rapidly cooled to room temperature in the atmosphere within the furnace. The exposure with excitation by the filtered 70 kvp X-rays was measured and was found to be 4.6 times that obtained with the calcium tungstate control and, thus, approx-imately 20 percent greater than that obtained with the phosphorprior to heating it in the atmosphere of argon and nitrogen.
A second ten-gram portion of the phosphor was heated for 2 hours at 925 C under the same argon-nitrogen atmosphere and -the speed was found to be 30 percent greater than with the untreated phosphor. A third ten-gram portion of the phosphor was heated in the same manner in a Corning Vycor boat for 3 hours at 825 C and the speed was found to be 15 percent greater~ Similar results were obtained by heating the phosphor in the carbon boat in a dry atmosphere of argon and nitrogen, that is, with use of the bubbler being omitted. However, when -11- ' * Trademark the phosphor was heated in t~e ~ycor ~oat with air passing through the bubbler in place of the mixture of argon and nitrogen, no improvement in the speed of the phosphor was obtained. A fourth ten-gram sample of the phosphor was placed in a quartz boat inside the carbon boat and heated for 3 hours at 825C with the mixture of argon and nitrogen passing through the water and a 30 percent increase in speed was obtained.
Planchets containing samples of the phosphors prepared in the manner described above were placed a distance of 54 inches from two fluorescent lamps and exposed for 30 minutes to a radiant flux of 70 microwatts per square centimeter.
As a result of this exposure, the X-ray speed of the europium-activated gadolinium oxide phosphors which had not been heated in a non-oxidizing atmosphere decreased by 25-29 percent. The speed of the phosphor heated in contact with carbon in a dry inert gas atmosphere decreased by 15 percent, while the speed of the phosphor heated in the absence of carbon in an atmos-phere of inert gas and water vapor decreased by 10 percent and the speed of the phosphors heated with carbon in an atmosphere of inert gas and water vapor did not decrease at all. Thus, the stability Of the phosphor to light is best when it is heated in the mildly reducing atmosphere generated by reaction of carbon with water vapor.
All gas flow rates specified in these examples where -measured at standard temperature and pressure and all speeds were determined as indicated in Example 1. ,~
Example 2 A terbium-activated gadolinium oxide phosphor was prepared in a manner similar to that described in Example 1.
In preparing this phosphor, a solution A was prepared by :,. . ..
.~ :. ..
- r -103~618 mixing 375 milliliters Or 2 molar gadolinium trichloride solution, 2 milliliters of 0.4 molar terbium trichloride solution, and 12~ milliliters of 37.5 percent hydrochloric acid with sufficient distilled water to make 5 liters of solution. A solution B was prepared by mixing 1125 milliliters of 1 molar oxalic acid with sufficient distilled water to make
distinguished from prior art processes in which oxide phosphors are heated in an atmosphere containing a halogenati~g agent, such as a hydrogen halide, in order to produce an oxyhalide phosphor. It is also carried out in an atmosphere which is free of chalcogenating agents, that is agents capable of forming sulfides, selenides or tellurides, as distinguished from prior art processes in which oxide phsophors are heated in an atmosphere containing a chalcogenating agent, such as the process of heating in an atmosphere containing hydrogen sulfide to form an oxysulfide phosphor. Heating in the non-oxidizing atmosphere is also carried out in the process of this invention in the absence of a flux and the invention thereby avoids the disadvantages involved in prior art pro-cesses in which fluxes have been employed.
The phosphors to which the method of this invention is applicable are oxide phosphors which have a host matrix of yttrium or of a rare earth metal, that is, a metal having an atomic number of from 57 to 71 in the Periodic Table of the Elements. These phosphors are activated by at least one rare earth ~' metal activator preferably selected from the group consisting of europium, gadolinium, terbium or dysprosium. Typical examples of the phosphors which can be prepared in accordance with the process of this invention to provide substantial improvement in properties such as X-ray speed are europium-activated gadolinium oxide ~Gd203:Eu), terbium-activated gadolinium oxide (Gd203:Tb), dysprosium-activated gadolinium oxide (Gd203:Dy), terbium-activated yttrium oxide (Y203:Tb), gadolinium-activated yttrium oxide (Y203:Gd), europium-activated lanthanum oxide (La203:Eu) and europium-activated yttrium oxide (Y203:Eu). The activator ~
. : .
~03~3618 forms a small proportion of the total phosphor, typically from about 0.01 mole percent to about 10 mole percent.
In preparing oxide phosphors in accordance with this invention, a preferred procedure is to employ the double-run co-precipitation method of United States patent 3,668,143 to form a mixed oxalate of the host and activator metals. In accordance with this method, separate aqueous solutions, con-taining (1) oxalate anions and (2) the host and activator cations, are separately introduced into a reaction solution, an excess of up to one molar of the anions or cations is maintained in the reaction solution throughout the reaction, and local excesses of anions or cations are prevented. Reaction temperatures are preferably in the range of from about 70 C
to about 100 C. It is preferred for the purposes of this invention to carry out the co-precipitation of the oxalates in the presence of excess oxalate ion and with at least a 0.2 molar hydrogen ion concentration in the reaction solution.
The separate solutions which are added to the reaction solution preferably have a concentration of less than 1 molar and most preferably less than 0.5 molar. Optimum results are obtained if the oxalate precipitate is prepared slowly, that is, with each solution being added to the reaction solution at a rate of less than 0.1 mole per liter of reaction solution per minute.
This results in the formation of large grain size oxalates which upon subsequent heating in an oxygen-containing atmosphere followed by heating in a non-oxidizing atmosphere provide oxide phosphors with desirable crystallographic structure and grain size which exhibit very high speeds.
As previously disclosed herein, the precipitate obtained by co-precipitating salts of the host and activator 1038~i18 m~tals i5 heated in an oxxgen-contain~ng atmosphere to form ~P oxide phosphor. Under typical circumstances this heating step is carried out in air although other ox~gen-containing atmospheres such as a mixture of oxygen and an inert gas such as argon could be used if desired. The duration of heating in the oxygen-containing atmosphere will ordinarily be in ~he range from about 0.5 hours to about 10 hours and more usually from about 1 to about 3 hours. Temperatures employed in this step are typically in the range from about 700C to about 1400C and pre-ferably in the range rom about 800C to about 11~0C.
After formation of the oxide phosphor by the step of heating in an oxygen-containing atmosphere, it is heated in a non-oxidizing atmosphere to bring about the desired improvement , in properties, such as X-ray speed. The atmosphere utilized in this step is a non-oxidizing atmosphere which is free of halogenating agents, chalcogenating agents, and fluxes. It may be an inert atmosphere, such as an atmosphere composed of nitrogen or o~ one of the inert gas elements such as helium, neon, or argon. Mixtures of two or more inert gases can be `~
utilized if desired. The atmosphere can consist of the dry inert gas or of a mixture of water vapor and inert gas. As an alternative to the use of an inert atmosphere, the atmos-phere employed in thiC step can be mildly reducing in nature.
Strongly reducing atmo~pheres are preferably avoided as they render the reaction difficult tp control and can adversely affect the phosphor, particularly when very high temperatures are employed.
An example of a preferred mildly reducing atmosphere that can be empioyed with good results is a mixture of hydrogen and an inert gas, such as nitrogen or argon in which the hydrogen is present in a minor proportion (i.e., less than about 455 by volume and preferably from about 5 to about 35% by volume).
~ . . . . . . . . .. . . . .. .
103~3618 A mildly reducing atmosphere that is especially useful can also be provided by heating the oxide phosphor in the presence of carbon, such as by placing the phosphor in a carbon boat, and providing some water vapor in the atmosphere. This results in the formation of water gas in accordance with the following reactions:
C ~ H20 ~ 2 2 ~ C02 2 The mildly reducing water gas atmosphere generated by the reaction of carbon with water vapor has been found to give excellent results, especially as regards the stability to light of the resulting phosphor.
In accordance with this invention, the oxide phosphor -~
is heated at an elevated temperature in a non-oxidizing atmos-phere, free of halogenating agents, chalcogenating agents, and fluxes, under conditions of time and temperature sufficient to effect an increase in the X-ray speed of the phosphor.
Suitable temperatures for use in this step are in the range from about 400 C to about 1400 C, with the higher temperatures within this range being used when the atmosphere employed is inert and the lower temperatures within this range being used when the atmosphere employed is mildly reducing. With inert atmospheres, the preferred temperatures are in the range from about 750C to about 1200C and most preferably in the range from about 800 C to about 1000 C. With an atmosphere con-sisting of a mixture of hydrogen and an inert gas, particularly good results are obtained with temperatures of about 450C to about 600C and the optimum temperature is about 500C.
Suitable times for heating the phosphor in the non-oxidizing atmosphere will depend on the atmosphere used, the temperature, . ..
and the thickness of the phosphor layer subjected to heating, but are typically in the range from about 0.5 hours to about 8 hours and more usually from about 2 to about 4 hours.
Heating of the phosphor in the non-oxidizing atmosphere does not cause sintering as occurs when phosphors are heated in contact with fluxes in accordance with the prior art. Accord-ingly, no grinding or similar operations are required in the process of this invention.
The steps of heating in the oxygen-containing atmos-phere and heating in the non-oxidizing atmosphere can be carried out in separate furnaces and this will ordinarily be ~ ;
the most convenient procedure. Alternatively, one can employ a continuous procedure in which the precipitate is passed into a two zone furnace, the first zone containing air, or other oxygen-containing atmosphere, and the second zone containing -the non-oxidizing atmosphere.
While applicant does not wish to be bound by any theoretical explanation for the manner in which his invention functions, it is believed that the heating in an inert or mildly reducing atmosphere alters certain sites within the crystal which act as absorbing centers for light. Studies of the emission spectra of the phosphors with excitation by X-rays indicate that these spectra are essentially unaffected by heat-ing in the inert or mildly reducing atmosphere except for an overall increase in intensity.
The invention is further illustrated by the following examples of its practice.
Example A europium-activated gadolinium oxide phosphor was prepared by use of the co-precipitation procedures described in United States patent 3,668,143 as follows:
.
103861~
A solution A ~as prepared ~y mixing 375 nilliliters of 2 molar gadolinium trichloride solution, 37.5 milliliters of 0.4 molar europium trichloride solution and sufficient distilled water to make 5 liters. A solution B was prepared by mixing 1600 milliliters of 1 molar oxalic acid solution with sufficient distilled water to make 5 liters. A solu~ion C
was prepared by mixing 200 milliliters of 2 molar gddolinium trichloride solution and 20 milliliters of 0.4 molar europium trichloride solution with s~fficient distilled water to make 4 liters. Solutions A and B were heated to 80C. Solution C
was placed in t~e fluted 22 liter flask de~cribed in United States patent 3,668,143 and heated to 95C. Solutions A and B were then simultaneously added to solution C at a rate of lO0 milliliters of each per minute and solution C was vigorously stirred during the addition. When the addition was complete, the precipitate was allowed to settle and was washed four times by decantation with distilled water. It was then colleated~land dried in air at room temperature overnight. The dry precipitate was placed in a quartz tray and heated in air for 1.5 hours at a temperature of 1115C ~n a muffle furnace and then rapidly cooled in air. The phosphor obtained by this procedure was placed in a m~tal planchet in the form of a layer with a thickness of 0.07& inch and an area o~ 0.76 square inches. A similar planchet was filled with a layer of a commercially a~ailable -calcium tungst~te pho~phor. The planchets were placed close to a sheet of black and white, high-speed, pan-sensitiz~d negative fi-lm (code 2043 Tri-X* recording film manufactured by Eastman Kodak Compan~ and exposed to 70 kvp X-rays filtered by 0.5 millimeters of copper and 1 millimeter of aluminum. After exposure, the film ' , , * Tradema~k ~ 10 -; ~ ... , .:
was developed, stopped, fixed, washed and dried in the con-ventional manner. The film was also exposed through an aluminum step wedge to determine the relationship between exposure and developed density. The exposure produced by the europium-activated gadolinium oxide phosphor with excitation by the filtered 70 kvp X-rays was found to be 3.8 times that obtained with the calcium tungstate phosphor used as a control.
A ten-gram portion of the europium-activated gadolinium oxide phosphor prepared in the manner described above was placed in a glassy carbon boat and was heated for 4 hours at 825 C in a tube furnace with 1.6 cubic feet per hour of nitrogen and 2 cubic feet per hour of argon passing through the tube. Before entering the furnace, the gas stream passed through a 500-milliliter capacity gas bubbler filled with distilled water. At the end of the heating period, the sample was rapidly cooled to room temperature in the atmosphere within the furnace. The exposure with excitation by the filtered 70 kvp X-rays was measured and was found to be 4.6 times that obtained with the calcium tungstate control and, thus, approx-imately 20 percent greater than that obtained with the phosphorprior to heating it in the atmosphere of argon and nitrogen.
A second ten-gram portion of the phosphor was heated for 2 hours at 925 C under the same argon-nitrogen atmosphere and -the speed was found to be 30 percent greater than with the untreated phosphor. A third ten-gram portion of the phosphor was heated in the same manner in a Corning Vycor boat for 3 hours at 825 C and the speed was found to be 15 percent greater~ Similar results were obtained by heating the phosphor in the carbon boat in a dry atmosphere of argon and nitrogen, that is, with use of the bubbler being omitted. However, when -11- ' * Trademark the phosphor was heated in t~e ~ycor ~oat with air passing through the bubbler in place of the mixture of argon and nitrogen, no improvement in the speed of the phosphor was obtained. A fourth ten-gram sample of the phosphor was placed in a quartz boat inside the carbon boat and heated for 3 hours at 825C with the mixture of argon and nitrogen passing through the water and a 30 percent increase in speed was obtained.
Planchets containing samples of the phosphors prepared in the manner described above were placed a distance of 54 inches from two fluorescent lamps and exposed for 30 minutes to a radiant flux of 70 microwatts per square centimeter.
As a result of this exposure, the X-ray speed of the europium-activated gadolinium oxide phosphors which had not been heated in a non-oxidizing atmosphere decreased by 25-29 percent. The speed of the phosphor heated in contact with carbon in a dry inert gas atmosphere decreased by 15 percent, while the speed of the phosphor heated in the absence of carbon in an atmos-phere of inert gas and water vapor decreased by 10 percent and the speed of the phosphors heated with carbon in an atmosphere of inert gas and water vapor did not decrease at all. Thus, the stability Of the phosphor to light is best when it is heated in the mildly reducing atmosphere generated by reaction of carbon with water vapor.
All gas flow rates specified in these examples where -measured at standard temperature and pressure and all speeds were determined as indicated in Example 1. ,~
Example 2 A terbium-activated gadolinium oxide phosphor was prepared in a manner similar to that described in Example 1.
In preparing this phosphor, a solution A was prepared by :,. . ..
.~ :. ..
- r -103~618 mixing 375 milliliters Or 2 molar gadolinium trichloride solution, 2 milliliters of 0.4 molar terbium trichloride solution, and 12~ milliliters of 37.5 percent hydrochloric acid with sufficient distilled water to make 5 liters of solution. A solution B was prepared by mixing 1125 milliliters of 1 molar oxalic acid with sufficient distilled water to make
5 liters. A solution C was prepared by mixing 100 milliliters of 1 molar oxalic acid and sufficient distilled water to make 4 liters. Solutions A and B were heated to 70C. Solution C
was placed in the fluted 22-liter flask and heated to 95 C.
After addgng 81.5 milliliters of 37.5 percent hydrochloric acid to solution C, solutions A and B were simultaneously added to solution C at a rate of 250 milliliters of each per minute.
Solution C was vigorously stirred during the addition. When the addition was complete, the precipitate was allowed to settle and was washed four times by decantation with distilled water. It was then collected and dried in air at room temp-erature overnight. The dry precipitate was:placed in a quartz tray and heated in air for 1.5 hours at a temperature of 1115C.
The resulting Gd203:Tb phosphor was rapidly cooled in air and -the X-ray speed was determined in the same manner as in Example 1. The exposure was found to be one third of that produced by the calcium tungstate control. When ten grams of this phosphor was placed in a carbon boat and heated for 4 hours at 825C in a tube furnace through which wet nitrogen and argon were passed under the conditions specified in Example 1, the exposure was found to be 6 times greater than that of the untreated phosphor.
A second ten-gram portion of the phosphor was placed in a Corning Vycor boat and heated for 2 hours at 500C with 1.6 cubic feet per hour of hydrogen and 2 cubic feet per hour of ~038618 argon passing through the bubbler and the treatment was found to increase the speed by a factor of five times.
Example 3 A dysprosium-activated gadolinium oxide phosphor was prepared in a manner similar to that described in Example 1.
In preparing this phosphor, a solution A was prepared by mixing 1 liter of 0.3 molar gadolinium trichloride solution, ~ milli-liters of 0.4 molar dysprosium trichloride solution and 49 milliliters of 37.5 percent hydrochlori acid with sufficient -distilled water to make 2 liters. A solution B was prepared by mixing 450 milliliters of 1 molar oxalic acid solution with sufficient distilled water to make 2 liters. A solution C
was prepared by mixing 75 milliliters of 1 molar oxalic acid with sufficient distilled water to make 4 liters. Solution C ~
was placed in the fluted 22 liter flask and heated to 95C. ~ -Then 81.5 milliliters of 37.5 percent hydrochloric acid was added and solutions A and B were simultaneously added to solution C at a rate of 100 milliliters of each per minute.
Solution C was vigorously stirred during the addition. When the addition was complete, the precipitate was allowed to settle, washed four times by decantation with distilled water, collected !~'' ' and dried in air at room temperature. The dry precipitate was placed in a quartz tray and heated in air for 1.5 hours at a -~
temperature of lllS C. The resulting Gd203:Dy phosphor was rapidly cooled in air and the X-ray speed was determined in the same manner as in Example 1. The exposure was found to be 0.8 times that obtained with the calcium tungstate control. When ten grams of this phosphor was placed in a Vycor boat and heated for 2 hours at 500 C in the tube furnace used in Example -1 with 1.6 cubic feet per hour of hydrogen and 2 cubic feet --14- `
103~618 of argon passing through the bubbler, the speed was found to be twice that of the untreated phosphor. The same improvement in X-ray speed was obtained when the phosphor was heated at 825 C
for 4 hours in a glassy carbon boat with 1.6 cubic feet per hour of nitrogen and 2 cubic feet per hour of argon passing through the bubbler. Similar results were also obtained with a dry atmosphere of argon and nitrogen.
Example 4 A terbium-activated yttrium oxide phosphor was prepared in a manner similar to that described in Example 1.
In preparing this phosphor, a solution A was prepared by mixing 1 liter of 0.3 molar yttrium trichloride solution, 30 milliliters of 0.4 molar terbium trichloride solution, and 49 milliliters of 37.5 percent hydrochloric acid in sufficient distilled water to make 2 liters. A solution B was prepared by mixing 450 milliliters of 1 molar oxalic acid with sufficient distilled water to make 2 liters. A solution C was prepared by mixing 75 milliliters of 1 molar oxalic acid with sufficient distilled water to make 4 liters. Solution C was placed in the fluted 22 liter flask and heated to 95 C. Then 81.5 milliliters of 37.5 percent hydrochloric acid was added and solutions A and B were simultaneously added to solution C at a rate of 100 milliliters of each per minute. Solution C was vigorously stirred during the addition. When the addition was complete, the precipitate was allowed to settle, washed four times by decantation with distilled water, collected and dried in air at room temperature. The dry precipitate was placed in a quartz tray and heated in air for 1 hour and 20 minutes at a temperature of 1000 C. The resulting Y203:Tb phosphor was cooled in air and the X-ray speed was determined in the same -1(~38618 manner as in Example 1. The speed was found to be 1/25 that of the calcium tungstate control. When ten grams of this phosphor was placed in a Vycor boat and heated for 2 hours at 500C in the tube furnace used in Example 1 with 1.6 cubic feet per hour of hydrogen and 2 cubic feet per hour of nitrogen passing through the tube (the gases used were dry as the bubbler was not employed), the speed of the phosphor was found to increase by a factor of 5.8 times.
Example S
A gadolinium-activated yttrium oxide phosphor was prepared in a manner similar to that described in Example 1.
In preparing this phosphor, a solution A was prepared by mixing 1 liter of 0.3 molar yttrium trichloride solution, 4 milli-liters of 0.4 molar gadolinium trichloride solution, and 49 milliliters of 37.5 percent hydrochloric acid in sufficient distilled water to make 2 liters. A solution B was prepared by mixing 450 milliliters of 1 molar oxalic acid with suf-ficient distilled water to make 2 liters. A solution C was prepared by mixing 75 milliliters of 1 molar oxalic acid with sufficient distilled water to make 4 liters. Solution C was placed in the fluted 22-liter flask and heated to 95 C. Then 81.5 milliliters of 37.5 percent hydrochloric acid was added and solutions A and B were simultaneously added to solution C at a rate of 100 milliliters of each per minute. Solution C was vigorously stirred during the addition. When the addition was complete, the precipitate was allowed to settle, -washed four times by decantation with distilled water, collected and dried in air at room temperature. The dry precipitate was placed in a quartz tray and heated in air for 1 hour and 20 ~-minutes at a temperature of 1000 C. The resulting Y203:Gd ,., . ,, , .. ~ . .
- - , .. , . ~ : .
1~)386~8 phosphor was cooled in air and the X-ray speed was determined in the same manner as in Example 1. The speed was found to be 0.23 times that of the calcium tungstate control. When ten grams of this phosphor was placed in a carbon boat and heated for 4 hours at 825 C in the tube furnace used in Example 1 with 2.0 cubic feet per hour of argon and 1.6 cubic feet per hour of nitrogen passing through the bubbler, the speed of the phosphor was found to increase by a factor of 1.6 times.
Example 6 A europium-activated lanthanum oxide phosphor was prepared in a manner similar to that described in Example 1.
In preparing this phosphor, a solution A was prepared by mixing 375 milliliters of 2 molar lanthanum trichloride solution and 37.5 milliliters of 0.4 molar europium trichloride solution with sufficient distilled water to make 5 liters. A solution B was prepared by mixing 1600 milliliters of 1 molar oxalic acid and sufficient distilled water to make 5 liters. A
solution C was prepared by mixing 200 milliliters of 2 molar lanthanum trichloride solution and 20 milliliters of 0.4 molar europium trichloride solution with sufficient distilled water to make 4 liters. Solutions A and B were heated to 80 C. Solution C was placed in the fluted 22-liter flask and heated to 95C. Solutions A and B were then simultaneously added to solution C at a rate of 100 milliliters of each per minute. Solution C was vigorously stirred during the addition.
When the addition was complete, the precipitate was allowed to settle, washed four times by decantation with distilled water, collected and dried in air at room temperature overnight.
The dry precipitate was placed in a quartz tray and heated in 1~38618 o air for 1 1/2 hours at a temperature of 1115 C. The resulting La203:Eu phosphor was cooled in air and the X-ray speed was determined in a similar manner to that described in Example 1. -The exposure produced was found to be 1.15 times that of the calcium tungstate control. When ten grams of this phosphor was placed in a carbon boat and heated for 3 hours at 92SC
in the tube furnace used in Example 1 with 2.0 cubic feet per hour of argon and 1.6 cubic feet per hour of nitrogen passing through the water in the bubbler, the exposure produced by the phosphor was found to be 1.35 times that of the calcium tungstate control. The reflectance spectrum of t~e Laz03:Eu phosphor, both before and after the heat treatment in the inert atmosphere, was compared with the reflectance spectrum of Eastman White Reflectance Standard barium sulfate. This -comparison indicated that heating the phosphor in the inert atmosphere increased the reflectance substantially in the region of wavelengths between 325 and 700 nanometers.
Example 7 ;
A europium-activated yttrium oxide phosphor was prepared in a manner similar to that described in Example 1.
In preparing this phosphor, a solution A was prepared by mixing 375 milliliters of 2 molar yttrium trichloride solution and 37.5 milliliters of 0.4 molar europium trichloride solution with sufficient distilled water to make 5 liters. A solution B was prepared by mixing 1600 milliliters of 1 molar oxalic ~ .-acid with sufficient distilled water to make 5 liters. A -~
solution C was prepared by mixing 200 milliliters of 2 molar yttrium trichloride solution and 20 milliliters of 0.4 molar europium trichloride solution with sufficient distilled water to make 4 liters. Solutions A and B were heated to 80C.
~.~)3~3618 Solution C was placed in the fluted 22-liter flask and heated to 95 C. Solutions A and B were then simultaneously added to solution C at a rate of 100 milliliters of each per minute.
Solution C was vigorously stirred during the addition. When the addition was complete, the precipitate was allowed to settle, washed four times by decantation with distilled water, collected and dried in air at room temperature overnight.
The dry precipitate was placed in a quartz tray and heated in air for 1 1/2 hours at a temperature of 1115 C. The resulting Y203 :Eu phosphor was cooled in air and the X-ray speed was determined in a similar manner to that described in Example 1.
The exposure produced was found to be 1.6 times that of the calcium tungstate control. When ten grams of this phosphor was placed in a carbon boat and heated for 3 hours at 925 C
in the tube furnace used in Example 1 with 2.0 cubic feet per hour of argon and 1.6 cubic feet per hour of nitrogen passing through the water in the bubbler, the exposure produced by the phosphor was found to be 1.9 times that of the calcium tungstate control. Measurement of the reflectance spectrum of the Y203:Eu phosphor in the same manner as in Example 6 showed that the heat treatment in an inert atmosphere brought about substantial improvement in the reflectance between 325 and 750 nanometers.
Example 8 A dysprosium-activated gadolinium oxide phosphor was prepared in a manner similar to that described in Example 1.
In preparing this phosphor, a solution A was prepared by mixing 750 milliliters of 1 molar gadolinium trichloride and 4 milli-liters of 0.4 molar dysprosium trichloride with 125 milliliters of 37.5 percent hydrochloric acid solution and sufficient --19-- : ' 103~618 ~
distilled water to make 5 liters. A solution B was prepared by mixing 1125 milliliters of 1 molar oxalic acid solution with sufficient distilled water to make 5 liters. A solution C was prepared by mixing 100 milliliters of 1 mola~r oxalic acid with sufficient distilled water to make 4 liters. Solutions A and B were heated to 70C. Solution C was placed in the fluted 22-liter flask and heated to 95C. Then 81.5 milliliters of 37.5 percent hydrochloric acid was added to solution C
followed by simultaneous addition of solutions A and B at a rate of 100 milliliters of each per minute. Solution C was vigorously stirred during the addition. When the addition was complete, the precipitate was allowed to settle, washed four times by decantation with distilled water, collected and dried in air at room temperature overnight. The dry pre-cipitate was placed in a quartz tray and heated in air for 1 1/2 hours at a temperature of 1115C. The resulting Gd203:Dy phosphor was cooled in air and the X-ray speed was .
determined in a similar manner to that described in Example 1.
The exposure produced was found to be equal to that of the calcium tungstate control. When 20 grams of this phosphor was placed in a carbon boat and heated for 3 hours at 925C in the tube furnace used in Example 1 with 2.0 cubic feet per hour of argon and 1.6 cubic feet per hour of nitrogen passing through the water in the bubbler, the exposure produced by the phosphor was found to be 2.3 times that of the calcium tungstate control.
Measurement of the reflectance spectrum of the Gd203:Dy phosphor in the same manner as in Example 6 showed that the heat treat-ment in an inert atmosphere brought about substantial improvement in the reflectance between 325 and 750 nanometers.
-20- ~' .. . ... , , .,. . .. ,, ., . : :
~xample 9 ~ 8618 Thirty-four grams of 99.99 percent gadolinium oxide was thoroughly mixed with 9.4 milliliters of 0.4 M europium trichloride (99.9 percent) in glass mortar, then dried at 100 C. After drying, the mixture was ground and ignited for 1 1/2 hours at 1115C. After ignition, the phosphor was tested in the manner described in Example 2 and the speed was measured in the manner described in Example 2, with the exception that the film was developed for 12 minutes in Kodak Developer D-l9 at 75 F. The exposure produced by this experimental gadolinium oxide phosphor with excitation by filtered 70 kvp X-rays was about l.0 X that produced by the commercial calcium tungstate phosphor.
Fifteen grams of the gadolinium oxide phosphor was , .
placed in the glassy carbon boat and ignited in wet argon and nitrogen at 925C for 2 hours (gas flow rates were 2.0 and 1.6 cfh, respectively, measured with flow meters calibrated with air). After cooling in the inert atmosphere, the sample was removed and the speed was measured as described before.
This measurement showed that the speed had increased to 1.5 X
that produced by the commercial calcium tungstate phosphor.
Fifteen grams of the gadolinium oxide phosphor was placed in a Corning Vycor boat and heated in hydrogen and argon for 2 hours at 500C (gas flow rates were 1.6 and 2.0 cfh, respectively). The phosphor was then cooled in an inert atmosphere and the speed was measured as described before.
This measurement showed that the speed had increased to 1.6 X
that produced by the commercial calcium tungstate phosphor.
Finally, fifteen grams of the phosphor was ignited in ;
30 a quartz boat in air for 2 hours at 1100 C. Again, the speed was about l.0 X that produced by the commercial calcium tungstate.
' ~,' *Trademark 103~618 Exposure of these phosphor samples to the ligh~ from two fluorescent lamps in the manner described before decreased the speed of the sample that had been ignited in air to a value that was 0.64 X that of the commercial calcium tùngstate, but had little or no effect on the speed of samples that had been heated in the inert or reducing atmosphere.
Oxide phosphors prepared in accordance with the method of this invention find utility in a number of fields, for example, in cathode ray tubes for television applications and in fluorescent lamps. However, they are especially useful in the preparation of intensifying screens for use in radgography.
Because of their high X-ray speed, they make it possible to decrease the speed and granularity of the radiographic film .
that is used to record the image. The intensifying screens can be used in film-screen combinations in which the film is double-coated or coated on only one side. The high speed of the phosphor also permits the use of abosrbing layers to provide cross-over control in double-coated films without excessive loss in system speed. These phosphors are also advantageous in intensifying screens because of their high density, typically in excess of 6 grams per cubic centimeter, which aids in providing improved radiographic sharpness without excessive mottle. The intensifying screens can be prepared in accordance with the usual practice in the art by dispersing the phosphor in a suitable binder, such as a copolymer of acrylic acid and an alkyl acrylate, a vinyl chloride polymer, polyvinyl butyral, a polycarbonate resin, and the like, and coating it on a suitable support such as a polyester film.
Good results are obtained with a phosphor to binder ratio on a weight basis of from about 4:1 to about 30:1 and more ~38618 preferably from about 10:1 to about 20:1 and with a phosphor coverage in the range of from about 15 to about 120 grams per square foot of screen and more preferably from about 30 to about 60 grams per square foot of screen.
An especially useful radiographic system employing the oxide phosphors prepared by the process of this invention consists of two intensifying screens, each having a coating of the phosphor dispersed in a binder, used in combination with a double-coated spectrally sensitized film that contains enough dye or other absorbing material to make the exposume of the back emulsion layer of the film less than 30 percent of the ,-total exposure of both emulsion layers when the film is exposed to X-rays with only a single screen in contact with the front emulsion layer. In tis combination, the high density of the phosphor improves the definition of the image that is produced and this improvement in definition is not obtained at the expense of system speed or mottle because the phorphor has high efficiency of fluorescence when excited by X-rays and for this reason relatively slow films with good physical characteristics and low granularity can be used.
The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the in~ention.
,'.." ~,-. .
was placed in the fluted 22-liter flask and heated to 95 C.
After addgng 81.5 milliliters of 37.5 percent hydrochloric acid to solution C, solutions A and B were simultaneously added to solution C at a rate of 250 milliliters of each per minute.
Solution C was vigorously stirred during the addition. When the addition was complete, the precipitate was allowed to settle and was washed four times by decantation with distilled water. It was then collected and dried in air at room temp-erature overnight. The dry precipitate was:placed in a quartz tray and heated in air for 1.5 hours at a temperature of 1115C.
The resulting Gd203:Tb phosphor was rapidly cooled in air and -the X-ray speed was determined in the same manner as in Example 1. The exposure was found to be one third of that produced by the calcium tungstate control. When ten grams of this phosphor was placed in a carbon boat and heated for 4 hours at 825C in a tube furnace through which wet nitrogen and argon were passed under the conditions specified in Example 1, the exposure was found to be 6 times greater than that of the untreated phosphor.
A second ten-gram portion of the phosphor was placed in a Corning Vycor boat and heated for 2 hours at 500C with 1.6 cubic feet per hour of hydrogen and 2 cubic feet per hour of ~038618 argon passing through the bubbler and the treatment was found to increase the speed by a factor of five times.
Example 3 A dysprosium-activated gadolinium oxide phosphor was prepared in a manner similar to that described in Example 1.
In preparing this phosphor, a solution A was prepared by mixing 1 liter of 0.3 molar gadolinium trichloride solution, ~ milli-liters of 0.4 molar dysprosium trichloride solution and 49 milliliters of 37.5 percent hydrochlori acid with sufficient -distilled water to make 2 liters. A solution B was prepared by mixing 450 milliliters of 1 molar oxalic acid solution with sufficient distilled water to make 2 liters. A solution C
was prepared by mixing 75 milliliters of 1 molar oxalic acid with sufficient distilled water to make 4 liters. Solution C ~
was placed in the fluted 22 liter flask and heated to 95C. ~ -Then 81.5 milliliters of 37.5 percent hydrochloric acid was added and solutions A and B were simultaneously added to solution C at a rate of 100 milliliters of each per minute.
Solution C was vigorously stirred during the addition. When the addition was complete, the precipitate was allowed to settle, washed four times by decantation with distilled water, collected !~'' ' and dried in air at room temperature. The dry precipitate was placed in a quartz tray and heated in air for 1.5 hours at a -~
temperature of lllS C. The resulting Gd203:Dy phosphor was rapidly cooled in air and the X-ray speed was determined in the same manner as in Example 1. The exposure was found to be 0.8 times that obtained with the calcium tungstate control. When ten grams of this phosphor was placed in a Vycor boat and heated for 2 hours at 500 C in the tube furnace used in Example -1 with 1.6 cubic feet per hour of hydrogen and 2 cubic feet --14- `
103~618 of argon passing through the bubbler, the speed was found to be twice that of the untreated phosphor. The same improvement in X-ray speed was obtained when the phosphor was heated at 825 C
for 4 hours in a glassy carbon boat with 1.6 cubic feet per hour of nitrogen and 2 cubic feet per hour of argon passing through the bubbler. Similar results were also obtained with a dry atmosphere of argon and nitrogen.
Example 4 A terbium-activated yttrium oxide phosphor was prepared in a manner similar to that described in Example 1.
In preparing this phosphor, a solution A was prepared by mixing 1 liter of 0.3 molar yttrium trichloride solution, 30 milliliters of 0.4 molar terbium trichloride solution, and 49 milliliters of 37.5 percent hydrochloric acid in sufficient distilled water to make 2 liters. A solution B was prepared by mixing 450 milliliters of 1 molar oxalic acid with sufficient distilled water to make 2 liters. A solution C was prepared by mixing 75 milliliters of 1 molar oxalic acid with sufficient distilled water to make 4 liters. Solution C was placed in the fluted 22 liter flask and heated to 95 C. Then 81.5 milliliters of 37.5 percent hydrochloric acid was added and solutions A and B were simultaneously added to solution C at a rate of 100 milliliters of each per minute. Solution C was vigorously stirred during the addition. When the addition was complete, the precipitate was allowed to settle, washed four times by decantation with distilled water, collected and dried in air at room temperature. The dry precipitate was placed in a quartz tray and heated in air for 1 hour and 20 minutes at a temperature of 1000 C. The resulting Y203:Tb phosphor was cooled in air and the X-ray speed was determined in the same -1(~38618 manner as in Example 1. The speed was found to be 1/25 that of the calcium tungstate control. When ten grams of this phosphor was placed in a Vycor boat and heated for 2 hours at 500C in the tube furnace used in Example 1 with 1.6 cubic feet per hour of hydrogen and 2 cubic feet per hour of nitrogen passing through the tube (the gases used were dry as the bubbler was not employed), the speed of the phosphor was found to increase by a factor of 5.8 times.
Example S
A gadolinium-activated yttrium oxide phosphor was prepared in a manner similar to that described in Example 1.
In preparing this phosphor, a solution A was prepared by mixing 1 liter of 0.3 molar yttrium trichloride solution, 4 milli-liters of 0.4 molar gadolinium trichloride solution, and 49 milliliters of 37.5 percent hydrochloric acid in sufficient distilled water to make 2 liters. A solution B was prepared by mixing 450 milliliters of 1 molar oxalic acid with suf-ficient distilled water to make 2 liters. A solution C was prepared by mixing 75 milliliters of 1 molar oxalic acid with sufficient distilled water to make 4 liters. Solution C was placed in the fluted 22-liter flask and heated to 95 C. Then 81.5 milliliters of 37.5 percent hydrochloric acid was added and solutions A and B were simultaneously added to solution C at a rate of 100 milliliters of each per minute. Solution C was vigorously stirred during the addition. When the addition was complete, the precipitate was allowed to settle, -washed four times by decantation with distilled water, collected and dried in air at room temperature. The dry precipitate was placed in a quartz tray and heated in air for 1 hour and 20 ~-minutes at a temperature of 1000 C. The resulting Y203:Gd ,., . ,, , .. ~ . .
- - , .. , . ~ : .
1~)386~8 phosphor was cooled in air and the X-ray speed was determined in the same manner as in Example 1. The speed was found to be 0.23 times that of the calcium tungstate control. When ten grams of this phosphor was placed in a carbon boat and heated for 4 hours at 825 C in the tube furnace used in Example 1 with 2.0 cubic feet per hour of argon and 1.6 cubic feet per hour of nitrogen passing through the bubbler, the speed of the phosphor was found to increase by a factor of 1.6 times.
Example 6 A europium-activated lanthanum oxide phosphor was prepared in a manner similar to that described in Example 1.
In preparing this phosphor, a solution A was prepared by mixing 375 milliliters of 2 molar lanthanum trichloride solution and 37.5 milliliters of 0.4 molar europium trichloride solution with sufficient distilled water to make 5 liters. A solution B was prepared by mixing 1600 milliliters of 1 molar oxalic acid and sufficient distilled water to make 5 liters. A
solution C was prepared by mixing 200 milliliters of 2 molar lanthanum trichloride solution and 20 milliliters of 0.4 molar europium trichloride solution with sufficient distilled water to make 4 liters. Solutions A and B were heated to 80 C. Solution C was placed in the fluted 22-liter flask and heated to 95C. Solutions A and B were then simultaneously added to solution C at a rate of 100 milliliters of each per minute. Solution C was vigorously stirred during the addition.
When the addition was complete, the precipitate was allowed to settle, washed four times by decantation with distilled water, collected and dried in air at room temperature overnight.
The dry precipitate was placed in a quartz tray and heated in 1~38618 o air for 1 1/2 hours at a temperature of 1115 C. The resulting La203:Eu phosphor was cooled in air and the X-ray speed was determined in a similar manner to that described in Example 1. -The exposure produced was found to be 1.15 times that of the calcium tungstate control. When ten grams of this phosphor was placed in a carbon boat and heated for 3 hours at 92SC
in the tube furnace used in Example 1 with 2.0 cubic feet per hour of argon and 1.6 cubic feet per hour of nitrogen passing through the water in the bubbler, the exposure produced by the phosphor was found to be 1.35 times that of the calcium tungstate control. The reflectance spectrum of t~e Laz03:Eu phosphor, both before and after the heat treatment in the inert atmosphere, was compared with the reflectance spectrum of Eastman White Reflectance Standard barium sulfate. This -comparison indicated that heating the phosphor in the inert atmosphere increased the reflectance substantially in the region of wavelengths between 325 and 700 nanometers.
Example 7 ;
A europium-activated yttrium oxide phosphor was prepared in a manner similar to that described in Example 1.
In preparing this phosphor, a solution A was prepared by mixing 375 milliliters of 2 molar yttrium trichloride solution and 37.5 milliliters of 0.4 molar europium trichloride solution with sufficient distilled water to make 5 liters. A solution B was prepared by mixing 1600 milliliters of 1 molar oxalic ~ .-acid with sufficient distilled water to make 5 liters. A -~
solution C was prepared by mixing 200 milliliters of 2 molar yttrium trichloride solution and 20 milliliters of 0.4 molar europium trichloride solution with sufficient distilled water to make 4 liters. Solutions A and B were heated to 80C.
~.~)3~3618 Solution C was placed in the fluted 22-liter flask and heated to 95 C. Solutions A and B were then simultaneously added to solution C at a rate of 100 milliliters of each per minute.
Solution C was vigorously stirred during the addition. When the addition was complete, the precipitate was allowed to settle, washed four times by decantation with distilled water, collected and dried in air at room temperature overnight.
The dry precipitate was placed in a quartz tray and heated in air for 1 1/2 hours at a temperature of 1115 C. The resulting Y203 :Eu phosphor was cooled in air and the X-ray speed was determined in a similar manner to that described in Example 1.
The exposure produced was found to be 1.6 times that of the calcium tungstate control. When ten grams of this phosphor was placed in a carbon boat and heated for 3 hours at 925 C
in the tube furnace used in Example 1 with 2.0 cubic feet per hour of argon and 1.6 cubic feet per hour of nitrogen passing through the water in the bubbler, the exposure produced by the phosphor was found to be 1.9 times that of the calcium tungstate control. Measurement of the reflectance spectrum of the Y203:Eu phosphor in the same manner as in Example 6 showed that the heat treatment in an inert atmosphere brought about substantial improvement in the reflectance between 325 and 750 nanometers.
Example 8 A dysprosium-activated gadolinium oxide phosphor was prepared in a manner similar to that described in Example 1.
In preparing this phosphor, a solution A was prepared by mixing 750 milliliters of 1 molar gadolinium trichloride and 4 milli-liters of 0.4 molar dysprosium trichloride with 125 milliliters of 37.5 percent hydrochloric acid solution and sufficient --19-- : ' 103~618 ~
distilled water to make 5 liters. A solution B was prepared by mixing 1125 milliliters of 1 molar oxalic acid solution with sufficient distilled water to make 5 liters. A solution C was prepared by mixing 100 milliliters of 1 mola~r oxalic acid with sufficient distilled water to make 4 liters. Solutions A and B were heated to 70C. Solution C was placed in the fluted 22-liter flask and heated to 95C. Then 81.5 milliliters of 37.5 percent hydrochloric acid was added to solution C
followed by simultaneous addition of solutions A and B at a rate of 100 milliliters of each per minute. Solution C was vigorously stirred during the addition. When the addition was complete, the precipitate was allowed to settle, washed four times by decantation with distilled water, collected and dried in air at room temperature overnight. The dry pre-cipitate was placed in a quartz tray and heated in air for 1 1/2 hours at a temperature of 1115C. The resulting Gd203:Dy phosphor was cooled in air and the X-ray speed was .
determined in a similar manner to that described in Example 1.
The exposure produced was found to be equal to that of the calcium tungstate control. When 20 grams of this phosphor was placed in a carbon boat and heated for 3 hours at 925C in the tube furnace used in Example 1 with 2.0 cubic feet per hour of argon and 1.6 cubic feet per hour of nitrogen passing through the water in the bubbler, the exposure produced by the phosphor was found to be 2.3 times that of the calcium tungstate control.
Measurement of the reflectance spectrum of the Gd203:Dy phosphor in the same manner as in Example 6 showed that the heat treat-ment in an inert atmosphere brought about substantial improvement in the reflectance between 325 and 750 nanometers.
-20- ~' .. . ... , , .,. . .. ,, ., . : :
~xample 9 ~ 8618 Thirty-four grams of 99.99 percent gadolinium oxide was thoroughly mixed with 9.4 milliliters of 0.4 M europium trichloride (99.9 percent) in glass mortar, then dried at 100 C. After drying, the mixture was ground and ignited for 1 1/2 hours at 1115C. After ignition, the phosphor was tested in the manner described in Example 2 and the speed was measured in the manner described in Example 2, with the exception that the film was developed for 12 minutes in Kodak Developer D-l9 at 75 F. The exposure produced by this experimental gadolinium oxide phosphor with excitation by filtered 70 kvp X-rays was about l.0 X that produced by the commercial calcium tungstate phosphor.
Fifteen grams of the gadolinium oxide phosphor was , .
placed in the glassy carbon boat and ignited in wet argon and nitrogen at 925C for 2 hours (gas flow rates were 2.0 and 1.6 cfh, respectively, measured with flow meters calibrated with air). After cooling in the inert atmosphere, the sample was removed and the speed was measured as described before.
This measurement showed that the speed had increased to 1.5 X
that produced by the commercial calcium tungstate phosphor.
Fifteen grams of the gadolinium oxide phosphor was placed in a Corning Vycor boat and heated in hydrogen and argon for 2 hours at 500C (gas flow rates were 1.6 and 2.0 cfh, respectively). The phosphor was then cooled in an inert atmosphere and the speed was measured as described before.
This measurement showed that the speed had increased to 1.6 X
that produced by the commercial calcium tungstate phosphor.
Finally, fifteen grams of the phosphor was ignited in ;
30 a quartz boat in air for 2 hours at 1100 C. Again, the speed was about l.0 X that produced by the commercial calcium tungstate.
' ~,' *Trademark 103~618 Exposure of these phosphor samples to the ligh~ from two fluorescent lamps in the manner described before decreased the speed of the sample that had been ignited in air to a value that was 0.64 X that of the commercial calcium tùngstate, but had little or no effect on the speed of samples that had been heated in the inert or reducing atmosphere.
Oxide phosphors prepared in accordance with the method of this invention find utility in a number of fields, for example, in cathode ray tubes for television applications and in fluorescent lamps. However, they are especially useful in the preparation of intensifying screens for use in radgography.
Because of their high X-ray speed, they make it possible to decrease the speed and granularity of the radiographic film .
that is used to record the image. The intensifying screens can be used in film-screen combinations in which the film is double-coated or coated on only one side. The high speed of the phosphor also permits the use of abosrbing layers to provide cross-over control in double-coated films without excessive loss in system speed. These phosphors are also advantageous in intensifying screens because of their high density, typically in excess of 6 grams per cubic centimeter, which aids in providing improved radiographic sharpness without excessive mottle. The intensifying screens can be prepared in accordance with the usual practice in the art by dispersing the phosphor in a suitable binder, such as a copolymer of acrylic acid and an alkyl acrylate, a vinyl chloride polymer, polyvinyl butyral, a polycarbonate resin, and the like, and coating it on a suitable support such as a polyester film.
Good results are obtained with a phosphor to binder ratio on a weight basis of from about 4:1 to about 30:1 and more ~38618 preferably from about 10:1 to about 20:1 and with a phosphor coverage in the range of from about 15 to about 120 grams per square foot of screen and more preferably from about 30 to about 60 grams per square foot of screen.
An especially useful radiographic system employing the oxide phosphors prepared by the process of this invention consists of two intensifying screens, each having a coating of the phosphor dispersed in a binder, used in combination with a double-coated spectrally sensitized film that contains enough dye or other absorbing material to make the exposume of the back emulsion layer of the film less than 30 percent of the ,-total exposure of both emulsion layers when the film is exposed to X-rays with only a single screen in contact with the front emulsion layer. In tis combination, the high density of the phosphor improves the definition of the image that is produced and this improvement in definition is not obtained at the expense of system speed or mottle because the phorphor has high efficiency of fluorescence when excited by X-rays and for this reason relatively slow films with good physical characteristics and low granularity can be used.
The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the in~ention.
,'.." ~,-. .
Claims (25)
1. In a process wherein a phosphor which has a host matrix of yttrium oxide or a rare earth metal oxide and is activated by at least one rare earth metal activator selected from the group consisting of europium, terbium, gadolinium and dysprosium, is prepared by heating a mixture of salts of said host and activator metals in an oxygen-containing atmosphere to form said phosphor; the improvement comprising the step of subsequently heating the phosphor at a temperature of between about 400°C and about 1400°C in a non-oxidizing atmosphere, which is free of halogenating agents, chalcogenating agents and fluxes, for a period of time suffi-cient to effect an increase in the X-ray speed of said phosphor.
2. In a process wherein a phosphor which has a host matrix of yttrium oxide or a rare earth metal oxide and is activated by at least one rare earth metal activator selected from the group consisting of europium, terbium, gadolinium and dysprosium, is prepared by heating a mixture of salts of said host and activator metals in an oxygen-containing atmos-phere to form said phosphor; the improvement comprising the step of subsequently heating the phosphor at a temperature of between about 400°C and about 1400°C in an atmosphere con-sisting essentially of an inert gas for a period of time suf-ficient to effect an increase in the X-ray speed of said phosphor
3. In a process wherein a phosphor which has a host matrix of yttrium oxide or a rare earth metal oxide and is activated by at least one rare earth metal activator selected from the group consisting of europium, terbium, gadolinium and dysprosium, is prepared by heating a mixture of salts of said host and activator metals in an oxygen-containing atmosphere to form said phosphor; the improvement comprising the step of subsequently heating the phosphor at a temperature of between about 400°C and about 1400°C in an atmosphere consisting essentially of a mixture of a hydrogen and an inert gas for a period of time sufficient to effect an increase in the X-ray speed of said phosphor.
4. In a process wherein a phosphor which has a host matrix of yttrium oxide or a rare earth metal oxide and is activated by at least one rare earth metal activator selected from the group consisting of europium, terbium, gadolinium and dysprosium, is prepared by heating a mixture of salts of said host and activator metals in an oxygen-containing atmosphere to form said phosphor; the improvement comprising the step of subsequently heating the phosphor at a temperature of between about 400°C and about 1400°C in the presence of carbon in an atmosphere consisting essentially of a mixture of water vapor and an inert gas for a period of time sufficient to effect an increase in the X-ray speed of said phosphor.
5. A process as described in claim 1 wherein said oxygen-containing atmosphere is air.
6. A process as described in claim 1 wherein said non-oxidizing atmosphere is a nitrogen atmosphere.
7. A process as described in claim 1 wherein said non-oxidizing atmosphere is an argon atmosphere.
8. A process as described in claim 1 wherein said non-oxidizing atmosphere consists of a mixture of argon and nitrogen.
9. A process as described in claim 1 wherein said mixture of salts of said host and activator metals is formed by co-precipitation.
10. A process as described in claim 1 wherein the step of heating in an oxygen-containing atmosphere extends for a period of about 0.5 hours to about 10 hours at a temperature of from about 700°C to about 1400°C.
11. A process as described in claim 1 wherein the step of heating in an oxygen-containing atmosphere extends for a period of about 1 hour to about 3 hours at a temperature of from about 800°C to about 1100°C.
12. A process as described in claim 2 wherein said phosphor is heated in said inert gas atmosphere for a period of about 0.5 hours to about 8 hours at a temperature of about 750°C to about 1200°C.
13. A process as described in claim 2 wherein said phosphor is heated in said inert gas atmosphere for a period of about 2 to about 4 hours at a temperature of about 800°C
to about 1000°C.
to about 1000°C.
14. A process as described in claim 3 wherein said phosphor is heated in said atmosphere of hydrogen and inert gas for a period of about 2 to about 4 hours at a temperature of about 450°C to about 600°C.
15. A process as described in claim 3 wherein said phosphor is heated in said atmosphere of hydrogen and inert gas for a period of about 2 hours at a temperature of about 500°C.
16. A process as described in claim 4 wherein said phosphor is heated in said atmosphere of water vapor and inert gas for a period of about 2 to about 4 hours at a temperature of about 800°C to about 1000°C.
17. A process as described in claim 1 wherein said phosphor is europium-activated gadolinium oxide.
18. A process as described in claim 1 wherein said phosphor is terbium-activated gadolinium oxide.
19. A process as described in claim 1 wherein said phosphor is dysprosium-activated gadolinium oxide.
20. A process as described in claim 1 wherein said phosphor is terbium-activated yttrium oxide.
21. A process as described in claim 1 wherein said phosphor is gadolinium-activated yttrium oxide.
22. A process as described in claim 1 wherein said phosphor is europium-activated lanthanum oxide.
23. A process as described in claim 1 wherein said phosphor is europium-activated yttrium oxide.
24. In a process wherein a gadolinium oxide phosphor activated by at least one rare earth metal activator selected from the group consisting of europium and terbium is prepared by (1) co-precipitating a mixture of salts of gadolinium and at least one of said activator metals and (2) heating said co-precipitated mixture in an oxygen-containing atmosphere to form said gadolinium oxide phosphor; the improvement comprising the step of heating the phosphor obtained in step (2) at a temperature of between about 450°C and 600°C in an atmosphere consisting essentially of from about 0 to about 45% by volume of hydrogen and from about 55 to about 100% by volume of an inert gas for a period of from about 2 to about 4 hours.
25. A process as described in claim 3 wherein said mixture comprises from about 5 to about 35% by volume hydrogen and from about 65 to about 95% by volume of an inert gas.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US37675773A | 1973-07-05 | 1973-07-05 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1038618A true CA1038618A (en) | 1978-09-19 |
Family
ID=23486351
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA202,818A Expired CA1038618A (en) | 1973-07-05 | 1974-06-19 | Process for preparing yttrium oxide and rare earth metal oxide phosphors |
Country Status (3)
| Country | Link |
|---|---|
| CA (1) | CA1038618A (en) |
| GB (1) | GB1465156A (en) |
| NL (1) | NL7409113A (en) |
-
1974
- 1974-06-19 CA CA202,818A patent/CA1038618A/en not_active Expired
- 1974-07-03 GB GB2950274A patent/GB1465156A/en not_active Expired
- 1974-07-05 NL NL7409113A patent/NL7409113A/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| NL7409113A (en) | 1975-01-07 |
| GB1465156A (en) | 1977-02-23 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US4032471A (en) | Process for preparing yttrium oxide and rare earth metal oxide phosphors | |
| US3795814A (en) | X-ray image converters utilizing lanthanum and gadolinium oxyhalide luminous materials activated with thulium | |
| US4507560A (en) | Terbium-activated gadolinium oxysulfide X-ray phosphor | |
| GB1595486A (en) | Phosphors | |
| US4107070A (en) | Process for improving the properties of oxysulfide phosphor materials | |
| JP2597695B2 (en) | Lu-Gd-Y-based phosphor and method for producing the same | |
| US5549843A (en) | Annealed alkaline earth metal fluorohalide storage phosphor, preparation method, and radiation image storage panel | |
| US3705858A (en) | Preparation of rare-earth-activated oxysulfide phosphors | |
| EP0011909A1 (en) | X-ray intensifying screen based on a tantalate phosphor and process for producing the phosphor | |
| US5227254A (en) | Photostimulable europium-doped barium fluorobromide phosphors | |
| JP2000192034A (en) | Production of phosphor | |
| EP0712917B1 (en) | Annealed alkaline earth metal fluorohalide storage phosphor, preparation method, and radiation image storage panel | |
| US4883970A (en) | X-ray intensifying screens containing activated rare earth borates | |
| US4608190A (en) | X-ray image storage panel comprising anion-deficient BaFCl:Eu/BaFBr:Eu phosphors | |
| JP3260541B2 (en) | Phosphor powder, ceramic scintillator and method for producing the same | |
| CA1038618A (en) | Process for preparing yttrium oxide and rare earth metal oxide phosphors | |
| US4929385A (en) | Freon free process for preparing a niobium activated yttrium tantalate X-ray phosphor | |
| EP0292616A1 (en) | X-ray conversion into light | |
| EP0257138A1 (en) | A process for the conversion of x-rays | |
| US6623661B2 (en) | Method for producing photostimulable phosphor | |
| US4925594A (en) | Hydrolysis resistance of rare earth oxysulfide phosphors produced by the addition of zinc in synthesis | |
| BE1000887A4 (en) | Crystal line with rare-earth metals light-activated fabric lanthaanoxidehalogenide. | |
| JPH032473B2 (en) | ||
| JP3249947B2 (en) | Rare earth fluoride based phosphor and radiographic intensifying screen | |
| EP0254836B1 (en) | Europium activated barium strontium magnesium fluorobromide photostimulable phosphor |